Clean rooms are increasingly used in industrial facilities for fabrication of precision electrical and mechanical components. Such rooms are typically pressurized so that contaminants, such as dust or the like, cannot enter when a door thereto is opened. The source of the pressurized air is usually a centrifugal fan mounted on the roof of the building that is operated in conjunction with a highly efficient particulate air filter.
In such applications, it is important that the air be moved at a controlled, low velocity. If the air is moved at a high velocity, it may stir up dust and other debris from within the room. Unfortunately, the air velocity through any given point in the ceiling is a strong function of that point's distance from the outlet of the fan. Further, the air velocity requirements may change with environmental changes or the use to which the room is put. A further requirement is that the air handling equipment should be quiet.
The prior art, while recognizing certain of these constraints, nonetheless has not provided a satisfactory air handling system for such clean room applications. It is an object of the present invention to provide such a satisfactory air handling system.
According to one embodiment of the present invention, a clean room is supplied with air at a controllable velocity from a blower with a variable damper mechanism. The ceiling of the room into which this air is to be routed is comprised of a plurality of panels of particulate filter material. Associated with at least some of said panels are air dampers comprised of first and second adjacent perforated plates. The first plate is fixed and the second plate is mounted for translational movement relative to the first. By moving the second plate relative to the first, the perforations therein are selectably opened or occluded, permitting the air passing through each panel to be regulated. Air flow through the room as a whole is controlled by the variable air flow feature of the blower.
In an alternative embodiment of the present invention, a third perforated plate is interposed between the first and second plates. The third plate serves as a gasket to limit air flow between the two plates and better seal the damper when the perforations are occluded. The seal formed by the third plate can be facilitated by introducing a slight upward bow in the second plate to thereby bias the second and third plates against the first plate.
The foregoing and additional objects, features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.